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Is it possible to lift a ship sized vehicle into the sky by following modern day aerodynamics and aircraft design?
Is it is possible in real life to make a aircraft carriers size ships to fly in the sky like the flying things we seen in avengers movie?

In theory you could build a huge airship or something that would have impressive physical size - but it wouldn't have a very high lifting capacity. The sort of thing in the movie is all sci-fi at the moment.  Actually there is a scifi stack exchange section you might like... ( http://scifi.stackexchange.com/ )

Like jet engines for jumbo jet,if we  can use a related proportion  engines to a vehicle of a size of aircraft carrier,will it raise and fly like a aeroplane. if it follows aerodynamic design.

Airborne aircraft carrier did exist, but were airship. I bet with today's (2015) technology, an aircraft carrier sized ship would also be some kind of airship such as the skycat.

I'm voting to close this question as off-topic because it is more suitable for SciFi.SE.

@SentryRaven I don't believe they'd accept it. They don't seem interested in questions about real-world physics.

@DanHulme Bah, real-world physics! Humbug!!

Possible: Yes
You can in theory lift anything. To do this you will simply need to generate an equal or exceeding amount of lift than the weight of the object. You will also need to generate enough thrust to achieve said situation. The closest thing I can think of to this was Howard Hughes Spruce Goose which did actually fly. If you are talking about the kind of vertical hovering that the ship in the movie does you would need to generate an amazing amount of thrust to achieve that. A US Nimitz-Class aircraft carrier displaces 100,000 long tons (224,000,000 LBS) so you would need to generate at least that much thrust but in reality you would need to generate more to overcome drag and to actually accelerate the craft vertically. For a point of comparison the Saturn V rocket weighed 3270 tons (6,540,000 pounds).
If we work through a quick example (these are very very lose numbers), lets take the Nimitz at 224,000,000LBS and the GE90 jet engine (currently the biggest turbo fan jet). The GE90 generates about 115,000 lbf of thrust. So it would take just under 2000 GE90s to generate enough thrust. But lets round it off at 2000 for ease of use and a bit of extra power. The diameter of the engine is 3.429m and the Nimitz is 332.8m long. You would need arms with 10 engines a piece just to make all 2000 engines fit down the length of the side. If they were stacked directly next to each other the arms would be about 35m in length. The bigger issue here is fuel flow/mass. You would need to lift enough fuel to actually power these engines for a useable amount of time.
On the more sifi side of things, you could use the Nimitz's nuclear reactor to power ducted fans which overcomes the fuel problem to an extent but I dont have any numbers on that.

is right, you could in theory lift just about anything if you solve the material and power problems. Why you would want to is beyond me though, all you'd be doing is floating a big target.

... Come on it's just impossible, and you know it.
Of course with infinite power you can achieve anything, but we live in a finite world.

Its not impossible at all, the weight is very quantifiable and the thrust requirements are easily calculated. While we may not be able to achieve it with modern avionics that does not mean that it would not be possible.

Adding 2,000 GE90 engines will also add at least an additional 40,000,000 lb of weight, not considering all the support structure and equipment needed, and then considering the thrust decreases with altitude...

Mount the engines along the sides (facing out) and deflect the thrust downwards. That might make the structure hot though...

You haven't calculated the fuel.  You need another 500 engines, or some such plucked from my patooty number, to lift the fuel for the other 2000.

I did not know the fuel burn for the GE90 but you are correct that the calculations are missing. Another 500, no big deal ;)

How many SRB's from the space shuttle would it take to lift a SMALL (WW II era) carrier? Disregarding all requirements for a soft landing...

@RalphJ, an Essex-class carrier displaces about a third what a Nimitz-class carrier does, so about a third as many -- or in concrete numbers, it looks like 26 SRBs.

It is important to note, that a sea-borne carrier is intentionally built from heavy materials for stability, so an air-borne carrier of similar size could probably have significantly lower weight.


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What is the aerodynamic reason that the An-225's vertical stabilizers are not simply vertical?

I am trying to understand the aerodynamic consideration that the two vertical stabilizers of this gigantic Antonov An-225 are not simply made vertical and are slightly pointing in. Then my questions are:

What is the reason?
What is the degree they lean?

I'm fairly sure (but have no sources to confirm) that the reasons are purely structural. The vertical stabilisers are simply set at a right angle to the horizontal one. This is just the easiest thing to do, and it also provides better clearance with deflected lower rudders. The aerodynamic consequences of this (for such small angles) are pretty minor.
Now there are good aerodynamic reasons to have dihedral on the horizontal stabiliser (which causes the whole tilt), but this is a different question, and it applies to many airplanes.

Some pretty good answers on horizontal stabilizer dihedral/anhedral here: https://aviation.stackexchange.com/q/26277/520

That also possible. But however, hard to believe such a multi millions dollar  cost airplane is just simply made without a very strong valid reason.

This is the strongest reason possible: it's cheap, easy and 'good enough'. Besides, remember that in Soviet economy, the question of efficiency was treated differently, and that An-225 was never meant to be produced in significant numbers: it's a quick adaptation of An-124.

I'd guess that they wanted to avoid an acute angle between the lower part of the vertical stabiliser and the horizontal - not for structural reasons but to limit interference drag.
They could have made the top piece vertical and just kicked out the bottom part, but then the rudder would have to have been made in two parts (or the hinge wouldn't have worked!)

Each rudder is in two parts anyway.

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Why does the A380 not have front windows on the top floor?
The title says it all.
On the 747, the cockpit is in the upper level and in the lower there's equipment (radar, avionics, etc.)
But on the A380, the cockpit is in the lower floor and there's no equipment in the upper floor. So I think it could be technically possible to place some front windows in order to get a pilot-like view.
I guess that would reduce the aerodynamic efficience of the aircraft, but maybe it could be compensated by higher prices on those exclusive view seats?
Has any aircraft like that ever existed or designed?

No doubt someone would buy it and just close the window shade...

People would be freaking out all day watching aircraft on the same airway pass above and below only 1000 ft away, on precisely the same line thanks to GPS.  When they are some way out, it looks like they are coming right at you.

It would be a front row seat for a birdstrike.

@JohnK - Do commercial flights really get within 1000 ft of each other?

@BruceWayne Minimium vertical separation 1000 feet, I would think so.  I have seen planes cross the flight path of planes I have been on by not much more than that much, although the less parallel the paths are the less likely for a direct intercept.

@BruceWayne yes that's what RVSM,  Reduced Vertical Separation Minima, is about.  Vertical separation of opposing tracks was reduced from 2000 to 1000 ft in RVSM airspace.  Because GPS navigation places everybody exactly on the airway center line, there no random left/right distribution of tracks and opposing planes go straight over or straight under.

If passengers wanted a pilot's-eye view (or even views of what the pilot can't see with the naked eye) there are other options, involving cameras and display screens, that would provide a more interesting experience. Microphones and speakers could be added as well.

Certification requirements require that there be an exit path both in front of and behind a passenger seat, so any seats with a view cannot be occupied during takeoff and landing. (The Boeing 747 does not meet this safety requirement because it is grandfathered in.) This is why the areas in front of the forward stairwell are used as a lavatory or lounge.

@user71659 that could be an answer!

@JohnK Approaching each other at 500 m/s, I doubt many passengers would even realize that there's an airliner there before it's passed them. Travelling in the same direction, the relative speed would be comparatively small.

@MichaelKjörling If you have a clear view to the front, you can spot oncoming aircraft when they are a few miles out because you see a little grey splotch of the head-on contrail with a black speck in the middle, and it grows.  As it gets closer you can tell it's on a line that is above or below your level but initially the effect is quite striking the first time you see it.

@JohnK I don't doubt what you're saying, though I have no direct experience with that myself; however, how many average passengers would make the connection? (No pun intended there.)

Most people woudn't take much notice I'm sure but somebody would get excited sooner or later lol.

@ymb1 Again, this is well known in the case of the 747, and why carriers have forward lounges in the A380. It is an interpretation by the FAA of the uniform exit requirement 25.807(c).

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Why are hexa airfoils used on rockets despite having more drag that diamond airfoils?
I was doing a study on airfoils shape for a rocket. I tested the diamond and the hexagonal airfoil with Missile DatCom, RasAero and the Shock Expansion theory and from my results it seems like the diamond is better (little more lift and noticeable less drag). Looking at other rockets design I found out that many actually uses hex airfoil, but I don't get why. Am I missing something? Any reason for that?
Also like 99% of rocket uses a sweep angle. If I remember correctly, having a sweep angle reduces the Mach number normal to the L.E., so using a sweep angle means that I'll have a subsonic flow normal to the L.E. even if the fligh Mach is supersonic. So, the L.E. should be rounded. Since all these rockets uses thin sharp airfoils, wouldn't the wing work better with no sweep angle?

I don’t think this is off topic here since it has to do with aerodynamics but you might try asking on the space exploration stack exchange if you don’t get the results you are looking for here.

This question is also asked on space exploration.

A rocket stabilized by fins alone needs a certain amount of lift at the rear to ensure that if it is disturbed from a nose-first attitude, it returns and damps out the resulting oscillation.  Adding mass at the rear of the rocket increases the amount of lift (hence fin area) required, as well as increasing the inertia factor that counters damping.
If a diamond fine provides little if any more lift, but weighs more (as it most likely does) than a flat-sided hexagonal section, it's probably a net negative in this compromise.  The added mass makes it harder to damp oscillation, and requires more area, which adds more mass.  Drag, on the other hand, helps a little (since it's near the rear of the vehicle, it tends to pull the tail behind the nose).
End result, for a rocket, it's likely that both on a lift/mass basis, and in consideration of drag, the flat-faced hexagonal fin shape is superior for overall performance.

Thank you for your answer! I'm beginning to understan the problem now. But why are you saying that the diamond weights more than the hex? Taken both with the same max thickness, wouldn't the diamond be lighter?

With the same thickness (and chord), the diamond would have flimsier edges.

Or with the same strength (which was my assumption) it would be heavier.


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Boeing Dreamliner MCAS
If it was not known that Boeing had new software in the Boeing 737 Max, do we know whether this same software is not in the 787-9?

Lack of initial research before asking question.

Stop..........just, stop.  I’m not feeding this.

@KorvinStarmast It’s not their power, it’s their geometry that required MCAS...

@KorvinStarmast That's a reason to downvote, not close.

@CptReynolds Fair point

No, we don’t know for sure. We do know, however, that it wouldn’t make any sense to install it.
It’s a bit like asking „are we sure the electric VW Golf doesn’t run the Diesel cheating software?“ - We don’t know, as the VW electric motor control code is not public (as far as I know), but it wouldn’t make much sense to fit it, right?


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What is the difference between flap load relief protection and overspeed protection?
What is the difference between flap load relief protection and overspeed protection?

According to this document/study guide

Flap Load Relief – on the 757 and a few 767s, if the flaps are at 30
  and Flaps 30 speed is exceeded, the flaps automatically retract to 25.
  On most 767s, if the flaps are at 25 or 30 and the placard airspeed is
  exceeded, the flaps automatically retract to 20. The flaps will
  automatically re-extend when airspeed is reduced. If the Flap Load
  Relief fails to operate when it should, the Trailing Edge light will
  illuminate and the FLAP LD RELIEF EICAS message will display

So flap load relief is a system that specifically protects the flaps. This is the result of accelerating to higher speeds.
Overspeed is a more general term and the actual speed that defines overspeed may vary with configuration, the 767/757 has a warning for that

Overspeed Warning – Master Warning, EICAS message, discrete light and
  siren when airspeed exceeds Vmo/Mmo.

It appears that overspeed protection is a function of the auto throttles.


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Is the combustion process in turbofans and turboshafts different?
According to a journal paper, for a Gnome turboshaft engine, fuel-air equivalence ratio decreases as power output increases. However, for a CFM56 turbofan engine, the opposite trend is true, and equivalence ratio increases as engine thrust increases.
Why is there such a difference between these two types of turbine engines?

Thank you. I have added an image of the data set in the question body above.

Please add the combustion chamber pressure at each data point. I suspect that you need a higher fuel-to-air ratio at low pressure to keep the combustion going, but without those pressure data this is just a guess. Also, besides the number of data points I fail to see the difference between turboshaft 1 and 2 - they have identical numbers.


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Could Airbus resume production of the A380?
Airbus is phasing out the production of their A380 superjumbo due to low demand from airlines. But what if (for the sake of argument) in the future Airbus' prediction of the need of a large aircraft to relieve congested hubs on popular route finally comes true and the need for a large aircraft comes up again? Could airbus resume production of the A380? They would probably have to upgrade the model to state-of-the-art technology (probably to an A380neo) to make it efficient enough to be attractive to airlines. What would Airbus need to do to put an A380 back on the market that would also satisfy the airlines' economic constraints (assuming there is demand for such a large aircraft)? Or would it be cheaper to develop a new model?

I'm voting this as off-topic. At the time of this question Airbus is still producing the A380, filling the existing orders - the run is ending because of a lack of sales as the design is incompatible with the market. Whether the market will change is a matter of opinion.

@GdD the question isn’t about our opinion of what the market will or won’t do, it’s about whether Airbus is going to be able to restart the production lines. Maybe someone knows what Airbuse’ policy is with regard to retaining knowledge of no longer produced planes, like the A300, and based on that can answer the question.

the first part of the question (could they resume) is answerable. The other questions about upgrades etc. are opinion-based. Remove those, and an answerable question remains.

@Hobbes: There are other examples (A320ceo->A320neo, A330ceo->A330neo, B737NG->B737MAX) where upgrades have been done. Someone with engineering knowledge might be able to extrapolate from there.

Your premise appears to be that the A380 is technically outdated, and an updated version could solve the economic issues. IMHO that is not the case.

@Sefe extrapolating is not what this stack is for.

Another option would the 747-8, the airline will also get a jumbo with enough capacity and four engines. The design phase started some years after the A380 and it's maybe still in a low production flow, thanks to the freighter variant. I assume that both, Airbus and Boeing are smart enough to keep the required engineers and tools ready for a follow-up generation. Nobody knows what the market will require in 2030, but I assume that metropolitan areas across continents still require a connection.

It turns out there's no need for extrapolation or speculation. Airbus already considered improvements to the A380 - and they weren't enough.

@Federico: Why not? It seems Hobbes is doing that pretty well in his answer.

@Sefe Hobbes has not extrapolated, as they said themselves. In general we don't appreciate extrapolation, since it invites speculations and opinions, and the SE model is not well suited for that.

How is it a matter of opinion whether they could resume production? The question is not about asking on an opinion whether the market changes, but whether Airbus could resume production, which is a fact. If it is opinion-based, please enlighten me how to rephrase it.

The parts about future upgrades and market demand is speculative, but if those were removed to leave only the question of whether restarting a production line is possible, it seems valid--and probably not very specific to the A380 at that point either.

@StephenS: There is no question about market demand. Market demand is assumed. The question is whether Airbus could resume production if there would be market demand. And it is also not speculative what in the aircraft's design was contributing to market failure (which is what Airbus would have to change).

The ability to restart production depends on:

is the tooling still available? Aircraft production uses giant jigs for production of the fuselage and wings. Sometimes these are stored when production ends (I've been in a hangar full of stored Airbus jigs), but sometimes they are scrapped.
is production space available? An A380 needs lots of space in the factory. If Airbus can use this floorspace to produce 3 A350s or one A380 per month, the question becomes what is more profitable for Airbus
is the infrastructure still available? The A380 was built at several sites, then assembled at Toulouse. Roads were widened to enable transporting the wings to the factory. Special vehicles were used etc. The French authorities won't start digging up the roads immediately, but in 10 years?

As noted in the comments, the A380 production line is still open, so it's easy to take new orders now. When the line closes, it becomes more difficult.

if the factory has been repurposed for other aircraft, you need to move your existing production to accommodate new A380 orders.
a few years after end of production, practical knowledge starts getting lost. The drawings etc. are still there, but things like optimal assembly sequences, how to move the giant wings in the most efficient manner, have to be rediscovered. When you assemble an aircraft every month for several years, you develop a routine. Restarting production means this routine has to be rebuilt, so the first year or so assembly will take more time and cost more.
when you close the production line, all contracts with suppliers also end. So they start clearing out their A380-specific tooling too. And when you restart, they need to retool and relearn, etc..

So the longer you wait, the higher the cost of restarting production will be. Upgrades can make the aircraft more attractive to customers, but developing the upgrade also costs lots of money ($1B to develop the A320neo), all of which you have to recoup by selling aircraft.
So it all comes down to how many orders you expect to get. A few dozen won't make it worthwhile to restart production once it's been shut down. A few hundred might.
Airbus has already worked on improved A380 variants. In 2015, they were talking about the A380neo:

On 15 June 2015, Reuters reported that Airbus was discussing a stretched version of the A380 with at least six customers. This aircraft, which could also feature new engines, would accommodate an additional fifty passengers. Deliveries to customers were planned for sometime in 2020 or 2021.[293] On 19 July 2015, Airbus CEO Fabrice Brégier stated that the company will build a new version of the A380 featuring new improved wings and new engines.[294] Speculation about the development of a so-called A380neo ("neo" for "new engine option") had been going on for a few months after earlier press releases in 2014,[295] and in 2015 the company was considering whether to end production of the type prior to 2018[291] or develop a new A380 variant. Later it was revealed that Airbus was looking at both the possibility of a longer A380 in line of the previously planned A380-900[296] and a new engine version, i.e. A380neo. Brégier also revealed that the new variant would be ready to enter service by 2020.[297] The engine would most likely be one of a variety of all-new options from Rolls-Royce, ranging from derivatives of the A350's XWB-84/97 to the future Advance project due at around 2020.[298][299]
On 3 June 2016, Emirates President Tim Clark stated that talks between Emirates and Airbus on the A380neo have "lapsed".[300] On 12 June 2017, Fabrice Brégier confirmed that Airbus will not launch an A380neo, stating "...there is no business case to do that, this is absolutely clear."

In 2017, Airbus announced the A380Plus:

The A380Plus, which was announced ahead of the Paris Airshow, will boast a new wing design intended to improve aerodynamics.
Airbus also said the cabin had been optimised to allow up to 80 extra seats "with no compromise on comfort".
The European plane maker said the new version would burn up to 4% less fuel thanks to its new winglets, which are designed to reduce drag. It will also have an increased maximum take-off weight and need less regular maintenance checks. Airbus said that along with other enhancements, the plane would cut costs for airlines by 13% per seat.

The fact they cancelled the programme in February 2019 indicates the A380Plus didn't get enough interest to justify keeping the production line open.


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Does load factor affect roll rate?
To be clear I am referring to a given aircraft at a given weight, speed, attitude, etc everything else the same except one is at say 0.5g and the other at 2.5g will there be a difference in roll rate if both have the same aileron deflection etc.
From my reading I think the answer is no but I am looking for something definitive. The question arises because the typical nose low UA recovery is UNLOAD then roll and recover to the horizon. For what reason is the UNLOAD? Some have suggested that it is because you will get a better roll rate to get the wings level. This I am not sure about.
I believe the main reasons for unloading are that (1) you want to avoid asymmetrical 'g' loads and (2) when holding a large amount of elevator force the pilots ability to input up to maximum aileron deflection is limited.
So I would appreciate someone confirming or denying if there is an aerodynamic reason that roll rate is affected by load factor?

There might be something here with gyroscopic physics, trying to pitch and roll at the same time.  This could be tested.  Rolling without pitching may allow the angular mass to accelerate in its plane undisturbed.  Pitching and rolling together (rapidly) may have undesirable motion coupling.

Are you excluding cases where roll control is accomplished in full or in part with spoilers ("spoilerons") rather than ailerons? It makes a huge difference to the answer, whether or not these cases are excluded or included.  "Unloading" the wing to well below 1G will greatly reduce the roll rate if roll control is accomplished mainly through spoilerons.

Load factor effects roll rate if you are at a speed close to stall. Then the outer part of the rising wing will be at a higher AOA, possibly beyond stall. You may even roll off on that side as the rising wing stalls and the other doesn't, departing controlled flight.
The other reason not to do a rolling pull, is if you find yourself fast, a rolling pull can overstress the wings and result in structural failure. So I guess you could say that is a roll rate limiter too, if your wing falls off.

Yes I agree with these thoughts. Still if the aircraft was slightly below Va would there be a difference in roll rate with a common aileron deflection at differing load factors?

I’d say no. As long as the rising wing where the aileron was located was below clmax, they would roll the same rate.

One of the best reasons to unload before using your ailerons is to make sure you are not
stalled.  If you are, using ailerons could reverse and make you roll the opposite way.
Ailerons can be evil when used uncoordinated with rudder, yet very helpful rolling out of an inverted dive.  The danger increases if the aircraft is yawing and near stall.  So it is much safer to recover in 2 steps, unloading first.

All I have is this extract from the Embraer 190 SOP guiadance for the nose down upset recovery
"It is important to reduce load factor while attempting to roll to wings level because it increases the roll effectiveness while decreasing the asymmetric loads on the airplane."

Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.


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Is this image of Compressor aerodynamics correct?

Image Source: Air Gas Turbine Technology by Treager, Chapter 5
The rotation direction of rotor shown seems opposite. If it is correct, these are the questions I would like to ask:

Why the Y vector is in opposite direction?
How will the pressure zones (high and low) will form on the rotor and stator airfoils?

Reminder to all: if you have an answer, post it in the answer field, not in the comments.

@Federico reminder has complicated a bit the answering process, but now we understand your actual problem, I can provide a focused answer immediately below, I've moved other elements at the end, you may ignore them as they were aimed to clarify your question and are indeed no more relevant.

If I consider Y as relative velocity, Then X should also be the same, though in opposite direction, right?
Good point, they are the same magnitude. There is some approximation in the drawing:

I am not able to understand the term defined by X
The convention used for velocities in this drawing seems to be: Velocities relative to rotors are drawn as dotted lines and velocities relative to stators are drawn as plain lines. As stators are fixed to the engine, plain line velocities may be seen as "absolute".

Y is the tangential velocity of IGV, and stators in general, relatively to the first stage rotor, and to rotors in general. Y is the apparent velocity of the stators.

X is the tangential velocity of R1 (first stage rotor) relatively to S1 (first stage stator). X is the true velocity of the rotors.

In the Note, the relative velocity is shown by D, which I think is similar to C, making C relative velocity

If you look at R1, there are arrows to emphasize the rotor channel is a diverging duct:

The channel slows down air and at the same time it increases pressure.

E described as "absolute" is linked to the fact it is relative to stator S1, which can be seen as being in the same reference frame than the engine, and "absolute".

D is the velocity of the flow relatively to R1, and E is the same velocity relatively to S1. The difference is: For the stator, D is affected by the rotation X.
For the rotor R1: C was transformed into D. D magnitude is smaller because of the deceleration by R1 diverging channel.
For the stator S1: B was transformed into E. E magnitute is larger because of the downwash created by R1.
As the mass is the same, and force is mass times acceleration, there is an excess of energy at the inlet of S1. This is the key to understand the compressor principle.

S1 stator channel is again a diverging duct. It converts the energy added by the rotation into pressure, slowing down air from E to F velocity:

This process ends here for the first stage, it will be repeated the same for the other stages, except IGV are not required, as the stator is designed to provide the correct angle of attack and velocity G for R2.

Bottom line, if we look at the process from the compressor standpoint, that is from the stators standpoint, for the stage R1/S1:

Air at the outlet of the stage has the same velocity it has at its inlet, F ≈ B
Pressure at the outlet is a bit larger than at inlet, due to addition of rotational kinetic energy (which source is the turbine, and ultimately fuel).
Adding stages allows to incrementally increase pressure. The pressure ratio of a stage is limited by the angle of attack on blades and vanes. Increasing pressure means decreasing (axial) velocity. A smaller axial velocity at the outlet conjugated with a constant X/Y tangential velocity increases the angle of attack on the next airfoil, possibly past the stall angle.

IGV have no velocity-to-pressure conversion function, their role is only to create the correct angle of attack for R1. The equal length arrows emphasize an IGV channel is neither diverging nor converging:

If the velocity magnitude at the first stage inlet has to be adjusted relatively to the ram velocity, with such IGV, this must be done by the engine inlet duct, prior to the IGV.
The stator vanes have a double role, the one explained above for IGV, and the one to convert energy added by X into pressure.

Your initial questions are answered  below.

Why the Y vector is in opposite direction?
Y velocity is the relative velocity of air for the rotor, it's opposed to the rotor actual rotation. It's like air coming from front when a wing moves forward:

How will the pressure zones (high and low) will form on the rotor and stator airfoils?
Blades and vanes are simple airfoils, which here are subject to chordwise winds C, E and G, exactly like regular wing airfoils. Pressure gradients will form like on any airfoil. E.g. for C and the first rotor blades, on the left your drawing, on the right the same drawing rotated:

Thank you, if I consider Y as relative velocity, Then X should also be the same, right? though in opposite direction, but in the Note in the figure, the relative velocity is shown by D, which I think is similar to C, making C relative velocity. Also, I am not able to understand the term defined by X.

I've added elements in the answer. I emphasized the difference between X and Y. X is the source of pressure in a compressor. X is converted into pressure by stators. That's the key to understand the compressor principle.

As far as I can tell, X and Y are the same length.

This one sort of reminds one of the physics quandary of whether light is a particle or a wave.  Let's treat the incoming air as a continuous energy wave.
One can see, although the incoming airflow is 90 degrees to the next part of the inlet/rotor/stator/rotor diagram, the trailing edge of the "top wing" would "bounce" the wave right into the oncoming next set of "wings" at the proper (relative) angle of attack.
Keep in mind there are a whole ring of "wings" for each stage, and that jet compressors can be "stalled" by a sudden change in inlet airflow (to be avoided).  This is why jet nacelles protect the compressor inlet.
At first the inlet vanes look "backwards", compared with the stator vanes, but the diagram is correct.  It may be questionable as to why they alternate solid and dashed lines for each stage discharge, but that can be figured out.

How will low and high pressure zones (high and low) .. form on the rotor and stator airfoils?

Pressure increases and volume decreases as air is compressed from top of the diagram to bottom.  In this case, higher pressure underneath the airfoils transfers the mechanical energy of the rotor into compressing the air.  Each stage compresses more and more. The stator "lines up" the airflow for another rotor pass.
Finally, the concept of "relative wind" can be reviewed for this application.  With ice boats, the (side wind) pushing the boat is not the same as that (from the movement of the boat) which creates the thrust from the sail, which allows it to go much faster than the wind.  The relative wind from the rotor (at thousands of rpm) would be the major vector.
It might help to draw the vectors to scale.

C, E, and G are the relative winds as 'seen' by the blades of the 1st stage rotor, the blades of the 1st stage stator and the blades of the 2nd stage rotor, respectively.
C is the result of the vector addition of B and Y
E is the result of the vector addition of D and X
G is the result of the vector addition of F and Y


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On C162 if I am at maximum elevator trim but still has control pressure is it normal?
Flying a C162 I have to set nose down trim to maximum, but I still feel pressure on the control and need to push the nose down.  Is this expected, or is weight & balance near the limit of the plane?
I checked the weight & balance and the CG is within limits but total weight is close to max gross takeoff weight.
Edited to add:
Weight & Balance info: (bracket indicated values that were used)

Basic empty weight 866.85, CG 131.97
Pilot (180), Arm 142
Pax (170), Arm 142
Fuel (80), Arm 143.26
No Baggage

CG location computed as:

Zero fuel weight 1217 lbs, CG at 134.7 ish
Takeoff weight 1289 lbs, CG at 135.3

I experienced residual control force at TAS around 80-100 knots.

At what speed in the airplane's speed range?

Stupid thing cruises at 110+kt and should trim to any speed up that speed.  There is no way the thing should require forward pressure to operate at cruise speed at full ND trim.  Something is bent, or the tab gearing is out of rig.  Or, it's just a crappy airplane.  I wouldn't want one.

It sounds as though the basic empty weight and moment calculated by maintenance personnel is not quite correct.  A Cessna 162 Skycatcher is certified under FAA FAR Part 23.

§ 23.2140 Trim.

(a) The airplane must maintain lateral and directional trim without further force upon, or movement of, the primary flight controls or corresponding trim controls by the pilot, or the flight control system, under the following conditions:

(1) For levels 1, 2, and 3 airplanes in cruise.
(2) For level 4 airplanes in normal operations.

(b) The airplane must maintain longitudinal trim without further force upon, or movement of, the primary flight controls or corresponding trim controls by the pilot, or the flight control system, under the following conditions:

(1) Climb.
(2) Level flight.
(3) Descent.
(4) Approach.

(c) Residual control forces must not fatigue or distract the pilot during normal operations of the airplane and likely abnormal or emergency operations, including a critical loss of thrust on multiengine airplanes.

Trim tab setting determines the angle of attack at which static stability forces in pitch (weathervaning tendency, in effect) will stabilize the plane hands-free.
As a proxy for angle of attack, pilots use indicated airspeed, since at a given C of G position and loading, a given angle of attack is found at a specific airspeed.
Although Part 23 is a bit vague with respect to trim speed in level flight, with G of G and total load in limits, the airplane should be able to trim hands-free to its normal cruising speed, or you have "residual control forces" which make the airplane unpleasant and distracting to fly at that speed.
So, if the plane can't be trimmed to its normal cruise speed, and C of G and loading is in limits, it's reasonable to suspect a problem with the trim rigging.
If the rigging and C of G and loading is good, then you are stuck with a plane that can't trim to its cruise speed, which is pretty strange. Your only option if you want hands-off stability is to reduce power to the speed at which the plane will fly level hands off, and use that as your cruise speed.

It is a Part 23 requirement to be able to trim at all CG ranges inside the envelope.

As the other posted answer with the quote from Part 23 says, just "level flight", which is open to interpretation. An airplane that can't trim to its cruise speed + some margin is a useless piece of equipment as far as I'm concerned. I've never experienced that, except in the case of a couple of homebuilts I've flown that had only fixed tabs, and therefore only one trim speed, and if you wanted to fly faster than the speed the fixed tab set, you had to hold forward pressure.I can't believe the Skycatcher is like that, but maybe that's one of the reasons they dumped the project after a few a/c.


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How long after the last departure shall the airport stay open for an emergency return?
For how long after the last take off for that day, will an airport stay open for emergency return of that last departed aircraft? Where can I find that recommendation?
To clarify: an airport needs to be closed during the night due to work-in-progress on a runway, so it can't stay open 24/7 for emergency landings.

If the airport will be closed for some time period in the US, there will be a NOTAM posted to the effect so pilots have plenty of warning.

@CrossRoads Not all airports are open 24/7, I think Petar is referring to airports that for example close at night

Airport is closed at night, but stay open 24/7 for emergency landings. In this particular situation need to be closed even for emergency landings due to work in progress on runway.

The airport where I work (not as a pilot or airport employee) was doing night work last summer, after their normal 10 or 11PM closing time, at the intersection of the 2 crossing runways.  There was  a NOTAM about it, so anyone calling for a weather briefing would have known about it.  Did they stay open later after the last departure?  I don't know.

What country are you asking about? If you're looking for a regulation it could vary by country.

@fooot Some regulation/recommendation from EASA/ICAO/IATA/ACI could be useful, if it exists.

Where I work, we have to stay in the tower for 15 minutes after the last departure in case they need to return. To my knowledge, there are no international regulations about this, so the rules may well be different from place to place.

@Fattie - though to be clear, this is an referenced fact, so it's more of an anecdote, and that is soooo internet. I'm not doubting the answer (especially given his long posting history and point count), but on the internet, anyone can claim to be anyone

I expect that to be highly situational to where the nearest divert field is. OAKland airport comes to mind.

@Harper That makes sense. At a remote location with no other major airports for a few hundred miles, closing the departure airport 15 minutes after takeoff would seem like a bad idea

@Harper Why does Oakland come to mind? SFO is ~11 miles away. What comes to mind for me is someplace like Easter Island, where you're the only diversion option for hours.

@Johnny Where I previously controlled it was the same (15 minutes). But ours was different to the tower 100 miles away that left as soon as you left their airspace.

ICAO Doc 4444 states the following:
7.15.4.1 Runway lighting shall not be operated if that runway is not in use for landing, take-off or taxiing purposes, unless required for runway inspections or maintenance.
7.15.4.2 If runway lighting is not operated continuously, lighting following a take-off shall be provided as specified below:
a) at aerodromes where air traffic control service is provided and where lights are centrally controlled, the lights of one runway shall remain lighted after take-off as long as is considered necessary for the return of the aircraft due to an emergency occurring during or immediately after take-off;
b) at aerodromes without air traffic control service or without centrally controlled lights, the lights of one runway shall remain lighted until such time as would normally be required to reactivate the lights in the likelihood of the departing aircraft returning for an emergency landing, and in any case not less than fifteen minutes after take-off.
So, RWY is definitely closed by NOTAM in some period due to WIP during night, and how long you stay open for emergency return of last departed aircraft is basically up to you. That's how I understood it.

Agree, it seems like it is up to the national authorities to interpret what "as long as is considered necessary for the return of the aircraft" means


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Why are radial engines louder than inline engines?
After visiting Oshkosh, I've noticed that radial-engine powered aircraft tend to be louder than in-line engine aircraft.
For example, watching a Ford Trimotor take off seems to be louder than most other aircraft I watched.

I would also wonder if a radial simply directs more noise towards where people tend to be observing and so sound louder even if the engine were not to put out more noise in an absolute sense.

To add to Max's answer:
All radial engines have an odd number of cylinders and the older ones had two-bladed propellers. So for a 7-cylinder radial, two turns of the prop would furnish 4 blade passages and 7 power pops from the exhaust. The blended result- seven beats against four- is not harmonically related and to our ears the result is more harsh and annoying.
Motorcycle engine designers know this and actually play with the crank timing and the vee angle between the cylinders on their V-twin engines to make them sound as rough and unpleasant (i.e., "badass") as possible.

A certain type of motorcycles I should add. Harleys (US brand, no surprise) in particular.

@SebastiaanvandenBroek, all the japanese manufacturers do this. My Kawasaki vulcan 1500 was designed for the best exhaust sound, then a counterbalance shaft was added to the engine to cancel the out-of-balance vibrations caused by the  crankshaft timing!

The Japanese manufacturers might do it, but they do it on their V-twin cruisers , which could be thought of as American style bikes.  The don't (routinely at least) do it on their sportier classes.  So @SebastiaanvandenBroek is thinking along the right lines, just considering manufacturers rather than markets

Though the reason for odd number of cylinders is so that the power strokes are distributed regularly. As a four-stroke engine fires on every second stroke, 7 cylinders allow a regular pattern of 1.3.5.7.2.4.6..

@JanHudec what’s less regular about 1 3 5 7 2 4 6 8? Or even 1 5 2 6 3 7 4 8? I suspect there’s more to it than regularity?

I suspect you are looking at a whole list of things that contribute to this in varying degrees, not one specific cause:

Some of the later radial engines were very large displacement engines
Almost no ability to tune the lengths of the exhaust paths individually to each cylinder
An era when there was less concern for noise abatement so effort wasn’t made
The size of the cooling fins and their direct exposure to your ears without having to pass through a cowling
Advancements in materials science in terms of what the cylinders are made of
Significant advancements in quality of ignition sparks, valve timing, and fuel chemistry

I actually think that last one may be one of the largest contributors.  Completion of fuel burn before the exhaust valve opens is harder to accomplish in large engines to begin with, and is only made harder by the limited technologies of the radial era.  Noise can often be a function of still having significant fuel burning when the exhaust valve opens.

The mere fact of being air-cooled not water-cooled, might contribute, too.  I've noticed water-cooled motorcycle engines seem to be muffled in their sonic emissions, compared to air-cooled ones.

Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.


text:
For large commercial jets is it possible to land and slow sufficiently to leave the runway without using reverse thrust or brakes
I have long wondered whether its possible (in theory at least) for jetliners under typical loading scenarios (pax and cargo), landing at a normal airport such as LHR to come to a slow enough speed to exit the runway just by using spoilers, full flaps and normal friction (air and tyres) i.e. no brakes and no reverse thrust ? Are the runways at commercial airports long enough for this scenario?
I understand that busy airports expect aircraft to leave the runway as soon as possible but I would still like to know if its theoretically possible.

Related: How much momentum is lost through the wheels when landing? and What are the relative braking contributions from wheel brakes, spoilers and thrust reversers?

Two real-world attempts: A320 lost brakes and even with reverse thrust ended up in the dirt in Ibiza. An A321 in Naples lost brakes, the crew didn't properly apply the emergency procedure, but they had reverse thrust, made a loop on an adjacent taxiway and back onto the runway.

@Flydog57 No power (engines) does not imply no brakes. The alternate brake system has a brake pressure accumulator with enough pressure for several brake applications even when all other hydraulics is lost.

it's possible for jetliners under typical loading scenarios... to come to a slow enough speed to exit the runway just by using spoilers, full flaps and normal friction (air and tyres) i.e. no brakes and no reverse thrust?

In this case, deceleration at landing is only due to aerodynamic drag and rolling resistance of the landing gears. As a first approximation we neglect the engine's thrust as well (which even at idle are anyway pushing the airplane, so a complete stop without brakes can be achieved only switching the engines off).
From Newton's second law $F=ma$ we simply get that the deceleration is $a=F/m$ where $F$ is the decelerating force due to the sum of the aerodynamic drag and the rolling resistance, as said.

For the drag we use the usual equation $D=½\rho V²SC_d$.
Rolling resistance is simply the weight times a coefficient $\mu$ which depends on the materials; $\mu=0.03$ is the standard value used for airplane tires on tarmac.

We get then:
$a=F/m=(½\rho V²SC_d + \mu mg)/m$
By definition, acceleration is the variation (derivative) of speed in time and that equation is therefore a differential equation which, without entering in mathematical details, possesses the solution:
$S_g=\frac{m}{\rho SC_d} \ln\left({(\mu+\frac{\rho SC_d V_{end}²}{2mg})}/{(\mu+\frac{\rho SC_d V_{td}²}{2mg})}\right)$
where:

$S_g$ is the ground roll length;
$m$ is the mass of the airplane at touchdown; in an emergency landing this can be as high as $0.85\times MTOW$;
$\rho$ is air density;
$V_{end}$ the final speed we want to reach;
$V_{td}$ the touchdown speed.

Let's do the math for an A380. Let's say that it touches down at some $m=330'000kg$, it reaches an end speed $V_{end}=0$ and has a touchdown speed $V_{td}=80m/s$ (150kts); for a jetliner in landing roll configuration a $C_d=0.03$ should be appropriate; as said typically $\mu=0.03$; the A380 as a wing area of $S=845m²$. Substituting we get:
$S_g=\frac{330'000}{1.125\times845\times 0.03} \ln\left((0.03+0)/(0.03+\frac{1.125\times 845 \times0.03\times 80²}{2 \times330'000\times 9.8q})\right)=7'667m$
A very long runway :-)
Obviously a lower weight, lower touchdown speed and/or higher rolling friction would reduce the ground roll: landing in wet grass ($\mu=0.08$) would for example reduce the A380's ground roll $S_g$ at less than 4'000m.

thank you @Sophit thats a facinating answer and I like that you used a real life example to illustrate the point. Just to tidy up my understanding - (A) do your workings calculate the length of runway needed to bring the airplane to a complete stop or just a typical runway exit speed ? I guess if complete stop then this would require quite a bit longer runway than exit speed ? (B) What does Cd represent in your equation ? (C) do the equations take into account the drag from the Flaps and Spoilers being down ?

@robbie70: thanks for your comment  (A) Yes, I considered a complete stop. If the end speed isn't zero then the equation changes a bit $\rightarrow$ I'll post the modified equation. (B)+(C) It's the drag coefficient. I've used 0.03 which is a reasonable number for a jetliner in landing roll configuration. I didn't specified it $\rightarrow$ I'll add it to the answer.

+1 for actually calculating the stopping distance! If you're bored, you could also calculate the remaining speed when reaching the end of a 3900m runway ;)

@sophit, 7667m?  That's shorter than either runway 17/35 or runway 15/33 at Edwards Air Force Base, though since that's salt pan rather than tarmac, your number for rolling resistance is off.  Edwards also has runways 07/25 and 18/36, at about 7000 meters each, sufficient if you're willing to do a rolling turnoff rather than a hard stop.

I think we can assume thrust reversers at idle thrust and still follow the spirit of the question

As I started reading, I thought, "here's a Peter Kämpf answer", but I was wrong! Yes, that's a compliment! Well done.

And landing in headwind will lower the stopping distance.
You can theoretically setup a situation where the plane has a ground speed of zero and still airborne if the wind is high enough, but that's not a scenario any pilot wants to find themselves in.

No, in the general case it isn't even close to possible.
You land a 60-ton aircraft at 120 mph, and it has to slow to (let's say) 30 mph in the space of (being generous) 2 miles, with no braking?  No way.
It's possible to stop an aircraft in most cases without the use of reverse thrust, and the difference between having or not having reverse thrust available is several hundreds of feet difference.  The rest of the stopping force comes from the wheel brakes, and without those, it would take miles & miles to slow down that much.
Take as an example, landing an airliner on runway 22 in El Paso (KELP), which at 12,000' long is one of the longest runways at commercial airports in the US. If you touch down normally & plan to exit near the end, it's common to stay off the brakes, and let the aircraft roll for a distance, before applying the brakes to slow down & turn off on the high-speed taxiway that takes you to the terminal.  During that time rolling, you're pretty much in the suggested state: idle thrust, no reverse, no brakes.  And from personal experience, I'll tell you that the aircraft isn't slowing very much.  I have no doubt at all that if a pilot were to never apply the brakes, the aircraft would roll off the far end of the runway, probably at 80+ knots (and that's after having initially applied reverse thrust for a while, to get from landing speed down to something close to 80 knots).
Is it possible to imagine a creative scenario involving immense up-slope on the runway, combined with strong headwinds, and maybe some other factor, that might result in getting the aircraft stopped?  Probably; a 50-knot headwind would work wonders for you in that sort of an exercise.  But how often do we land with that sort of a headwind?  Almost never.
The main function of deploying spoilers on landing isn't the drag, although that's a secondary benefit.  The main purpose is to kill the creation of lift from the wings, so that the entire weight of the aircraft is on the wheels, allowing them to brake harder without (or, before) skidding.  If you had 60 tons of mass, being stopped with wheels that only have 10 tons of weight on them, the wheels would skid (or the anti-skid system would release the brakes to prevent the skid) before you could generate much in the way of stopping force.  But if you have the whole weight of the aircraft on them, then you can apply the brakes much more firmly.  That's why deploying spoilers is important on landing, much more so than the aerodynamic drag that they provide.

Common belief is that reverse thrust is needed, or that it's used to reduce brake wear. What I have read is that as you said in most cases on a dry runway reverse thrust isn't needed. Apparently it's mainly used to avoid brake overheating which can increase turnaround time waiting for the brakes to cool off. Apparently the wear on brakes is less expensive than the fuel burned and wear on the engines using reverse thrust, so some airlines prefer using idle reverse thrust when possible, which contributes very little to braking but at least there's no forward thrust.

Note that a strong headwind would help you in two ways.  It slows you down once you've landed, of course;  but also your groundspeed can be correspondingly lower at touchdown, giving you less speed to get rid of on the runway.

@MichaelSeifert No, it only helps you one way.  You are counting the same effect twice.  Your reduction in groundspeed is based on the wind speed relative to the ground.  But the wind relative to the aircraft is the same in both situations, so there is no added slowing effect.

@KurtFitzner: If a headwind were to start just as the plane touched down, it would improve the effectiveness of aerodynamic drag mechanisms.  Likewise if a headwind dissipated just as a plane touched down, the effectiveness of aerodynamic drag mechanisms would be decreased, but the amount of kinetic energy to be dissipated would still have been reduced prior to touchdown.

Not only is thrust reverse not needed, @StevePemberton, testing and certification of the braking system is done without thrust reverse at all. The brakes are required to be able to stop the aircraft without any engine assistance. That is how the landing rollout tables are built.

@supercat That's correct but not relevant to the general case of a strong headwind and whether it helps by slowing you down and also by reducing your groundspeed.  Which the same wind can never do together.

@KurtFitzner why would it not be able to? As supercat pointed out, the two effects occur at different times. There's no double counting. When flying you're in the reference frame of the air, so the headwind reduces your groundspeed when you're at touchdown airspeed. When you're on the ground, you're in the earth's reference frame, and the wind continues to oppose the remaining velocity. Really not sure what double counting you think is happening.

It's theoretically possible but in most cases not practically possible due to the limited runway length available. If the aircraft was very light (low threshold speed) and there was a strong headwind with an up slope then on a very long runway you could get down to a fast taxi speed.  The problem at light weights is that your thrust at idle will tend to prevent slowing down to and maintaining  taxi speeds without using the brakes or idle reverse. I've done it when the conditions were right on a very long runway. Not exactly SOP though!

To complement the other answers with a summary:
No. Aerodynamic braking doesn't work well at low speeds. On a very long runway, it could at best slow the plane down to a non-lethal crash. Spoilers also don't produce as much drag as the huge brakes that jet fighters use - and fighters still need brakes or a parachute for a full stop.
However, transport category aircraft are required to be able to stop using brakes alone, no reverse thrust. They are also generally designed to be able to stop within the length of a runway using reverse thrust alone, no brakes.
This is for a runway. In a rough field, the stopping power from uneven terrain is stronger and sufficient for a full stop.

Yes, it can be done. A medium jet slows down easily on light to moderate headwinds on a 4000m runway without reverse and wheel brakes to vacate via highspeed exit at the end of the runway.
And before someone comments, yes one should open reverse cowls (ie. idle reverse) and try out the brakes at safe distance remaining just to make sure they are there if required. And it is polite to make sure nobody is behind you so the next crew doesn’t have to squeeze their muscles in anticipation waiting if you vacate the runway in time or not :)

thank you for your answer @busdriver - I have to admit my gut feel was that this could be possible - although you do say this is for a medium size jet - would this include, jets in the class 757, 767, A330 or A321/A320/737 ? Am I correct in thinking you are a professional airline pilot ?

This information is incorrect.  With no braking, you aren't going to be close to taxi speed before the end of a normal runway, unless something very unusual (massive headwinds, extraordinary upslope, etc) is going on.


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Would it be feasible to restart production of the F-20 Tigershark?
This seems unlikely considering the cancellation of the F-20 program, however, the F-20 has been characterized as "the right fighter at the wrong time". As such, I'm curious if F-20 production could be restarted to provide a cheap, easy to operate fighter to support a major war effort (in this case a theoretical conflict over Taiwan) as an alternative to more expensive aircraft such as the F-16.

In 1983, the cost of an F-20 was around 10% less than the cost of an F-16. The 1983 cost of an F-20 inflation adjusted to 2022 dollars would be higher than the current 2022 cost of an F-16. You might say that’s not a fair comparison, but it might be apt, because starting F-20 production would involve one-time costs to create or change production lines to be able to make the aircraft. So it’s not a given that restarting F-20 production would actually be cheaper per aircraft than current F-16 production. And the F-16 is currently excellent value for the money in modern multirole aircraft.

JF-17 is basically a further modernized F20 in concept. JF-17 grew out of Super-7 and Super-7 is basically Grumman's effort to transplant the upgrades between F20's and F5 onto a J-7/Mig-21. So why not just buy JF-17?

There was no "production line" for the F-20, that I know of.  Hence there is nothing to restart.  And there was no program, as such, to cancel.  Northrop developed that airframe on it's own nickel.

Interesting, but way too late.
The F-5 was an amazing fighter for its time. It wasn't based on Energy-Maneuverability, but in many ways, its airframe and design concept do resemble a 4th generation light fighter.
However, in 1980, the actual F-5 did not perform at all against Soviet aircraft such as the MiG-21 and MiG-23. Skipping the -25, as it's on another level altogether. Most likely, the F-5 just didn't have enough thrust and enough radar resolution to beat these. The big heavy F-14 did succeed.
The F-20 prototype had a single turbofan engine that far exceeded the TWR of the F-5's dual turbojets. The issue is, this engine was meant for larger aircraft, such as the F-8 and potentially an F-16 competitor. Would the F-20 have survived into production without gaining weight?
Unlikely. The F-5's avionics were also out of date, as seen by the 0:10 kill ratio against MiG 21-25. Chinese MiG-29 and Su-27 clones are an entire generation ahead of these. More extensive sensors and armament, necessary to compete, would have burdened the F-20 up considerably.
The F-5 and the F-20 were both great. They had all the potential, in their time, and were ahead of it. The F-20 would still be a very competent fighter kinematically.
The issue of concern is avionics capability and related costs. Modern fighters have the majority of their cost in avionics. Their weight is also considerable (2-3 tons in the teens era, but probably more today), and avionics are the one thing that doesn't scale with airframe size.
If modernized to carry the same generation of avionics as the latest fighter upgrades, the new F-20's cost would be at best 30% lower than that of newest F-15 or F-16 variants. With old F-5 avionics, they'd be cannon fodder to anyone who can get at least a MiG-21bis, and that's anyone these days.
In short, the importance and the cost of avionics mean that the marginal cost of heavier airframes is less significant that it used to be. High kinematic performance and a larger armament load they offer still matter. This favors larger heavier fighters from a price/performance perspective.
The light fighter niche today is mostly occupied by the Saab Gripen and the HAL Tejas. The Gripen weighs about the same as a new F-20 would, carries modern avionics, and has been polished by 25 years of reliable experience. The Tejas is new and comes from India, making procurement less politically complicated. Any new competitor would have to offer something they don't have. And it's hard to think of something neither of them has that is feasible on a smaller budget.

That's all very interesting, thank you for the detailed answer!

“ The issue is, this engine was meant for the 2x larger F-16.” Actually the F8 was the aircraft that use the GE F404 engine, not the F-16.

@CarloFelicione Well, it was meant to power larger aircraft, comparable to it... But not the production F-16 itself, true, I'll edit.

There certainly is a market for a lightweight fighter similar to the F-20, combining basic low observable technology, a simple, easy to maintain engine and with good but ‘no frills’ modern mission systems.  The F-20 has a lot of excellent earmarks in that respect and would make a good template to start from.  As to bring back the F-20 and beginning production on that again, that’s not likely.  It was quite a risk for Northrop to do that in the 1980s and cost them \$3 billion in R&D (an absolute bargain compared to the F-35’s bloated \$405 billion R&D budget) and all for naught.

Given how costly and time consuming it is to produce and maintain pilots, it seems that the future of warfare is more of the expendable drones, than cheap airplanes that easily lose pilots. Estimated at $6+ million dollars to train a US pilot.
This is in addition to the valid points other good answers list. Supporting yet another airplane type has a lot of inherent costs that a hypothetical saving of 10% or even 20% can hardly justify.
Update: a video part of which goes over expenses for different airplanes and pilots. See chapters "Economics of Unmanned Systems" and "The Pilot".

This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review

@Vikki: This definitely answers the question: "No". It even gives two reasons why not. Note that the question already establishes economic criteria ("cheap")

@MSalters: Without any sources to back up their speculation, this cannot be regarded as a useful answer, and should've instead either been posted as a comment or fleshed out into an actual answer.

@Vikki, most answers do not have any references. Not I defend this but this is also not wikipedia and one can check facts based on an answer and improve it or add another answer. And/or downvote if answer was incorrect based on facts discovered. In any case I accidentally saw an interesting video about drones that covers this in some way so I added it to the answer.


text:
What is that ceiling compartment of a Boeing 737?
Does somebody know what that big box in the roof of the 737 cabin is?

That should have been explained during the safety brief, I think...

It holds a life raft. In case of ditching in the ocean, the raft would be removed from that compartment and tossed into the water, where it would inflate.

Has that actually ever been performed, or is it more of an theoretical option?

@vidarlo  Off the top of my head, I can't think of any time it's been used, but that doesn't mean that it never has. Might actually be a worthwhile question in its own right.

@vidarlo: AFAIK, there haven't been many ditchings of an airliner, and even less successful ones. It shouldn't be hard to go through all of them and check whether at least one raft was deployed.

I believe that this compartment is meant to hold a life raft, but I have seen it many times being used just for storing items like pillows and covers or even hand luggage if they run out of other space.

Followup: https://aviation.stackexchange.com/q/65614/1360


text:
Why is the 737 so low?
Why does the Boeing 737 sit so low on its wheels compared to the Airbus A320?

Related:Is there less vertical space for an engine under the wing of a 737 Max than for an A320neo?

I have a feeling „because its landing gears are shorter“ is not quite what you’re after...?

Low rider style for cruising the boulevard...

Wendover actually just came out with a very relevant and interesting video just on that here: https://www.youtube.com/watch?v=BfNEOfEGe3I. He goes into good detail on the reasons for it and modifications made to evolve it along its lifespan. Check it out for a great overview on the history and future of the 737.

For everyone voting to close this question, please see ymb1's post here: https://aviation.meta.stackexchange.com/questions/3802/question-closing-is-too-arbitrary?cb=1 !!

@CptReynolds Well, no. That just defers the question to why is the landing gear shorter?

@DavidRicherby ... to which the rather obvious answer would be „because that was the option selected by the designers“! (in case it wasn’t clear, I was joking...).

The 737 was originally designed to be a smaller aircraft serving more regional routes. The original JT8D low-bypass turbofans easily fit under the wings, and allowing the plane to sit lower to the ground made it easier for the plane to operate at smaller airports without support equipment. Passengers could use the built-in air stairs and the cargo bay was low enough that ground workers could climb in to load and unload baggage.
The low height also allowed shorter and lighter landing gear. The 727 had tail-mounted engines which allowed it to sit lower to the ground, so keeping the 737 low helped to keep some commonality there as well. Over time the airplane has grown longer, been fitted with larger diameter engines, and become capable of much longer flights.
The A320 was designed from the start for the larger family of CFM56 high-bypass engines. The main competition was the 737 Classic version, which was powered by similar engines and had grown substantially from the original 737 versions. Both planes ended up in a market where the low height of the 737 didn't have as many advantages.

The follow up question "why don't they just make the gear longer?" was covered somewhere else around here, but summarized is: Because longer gear need more storage area & mounting point strength which leads to modifications that make it no longer "just like all the other 737s ever produced" (as well as lots of FAA approvals). This makes it less appealing to airlines who see it as having to train pilots on a new air frame.


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Is it legal to build your own plane and fly it?
Is it legal to build and fly your own airplane? This essentially leads to two central questions: Will the FAA even let you build and fly your own airplane?, and Will there need to be inspections and testing records to certify it as flightworthy and legal before being able to fly it?
Say I built my own plane, a large plane. 3 Propellers powering the plane. Amphibious, can land and take off on a runway or on the water. It's red, if this makes any real difference. And it is built to support 2 people and is supposed to be able to fly for up to 1 week without refueling. That being said, if the plane crashes it'll cause quite some damage. And to fly for 1 week supporting 2 people and quite a lot of cargo in the form of food and other essentials, the airplane is loaded with fuel.
If I know the plane floats on the water, could I fly it in an unpopulated area in short testing runs, or is that considered illegal? This also brings the question, Is there is a limit to how much fuel a plane can legally carry in a single flight? Any help would be much appreciated.

Have you read through the FAA regulations (in the FARs) concerning experimental aircraft? Limitations are pretty clearly spelled out...

Could you link those regulations, by chance? That would help quite a lot. Thank you.

Most of your challenges will be from the laws of physics, not the FAA.

There is an irreparable conflict with realms of regulations and physics here. According to regulations building and flying is totally possible (albeit extremely laborous, accounting for design, building and the red tape), but the plane described is not possible, not if the specified week of operating consists of even 1/10 of flight time (~17 h). Twin Otter as an example: fuel burn ~575lb/h, fuel capacity ~2500lb, max weight ~12500lb, so fuel about 20% of max w. for 17 h of flying you'd need ~10000lb of fuel, so very rough estimate of max w is about 50000lb. IRL it's even worse.

@ob318 There is no reason to put "under FAA regulations" into the title, as the question is already tagged such. Per this StackExchange Meta question it is simply not needed, even for search engine optimization.

Yes, it's legal. The FAA has an amateur-built aircraft homepage with links to regulations, guidance etc.
It's also very common. The Experimental Aircraft Association has a lot of resources too.

But can I fly the plane without completing those forms? And another question for people with a similar issue but that don't have pilot licenses, Could a person fly their own plane without a pilot license? (The controls could be all wack, being however the builder wanted it)

@Ginger In the US, you can't "operate" an "aircraft" (definitions in 14 CFR 1.1) unless it's registered (14 CFR 91.203(a)) and you have a pilot's certificate (14 CFR 61.3(a)). Ultralights are exempt from those requirements. Flying without a pilot's certificate is not recommended.

Needless to say, the concept in question here will not fit the ultralights category :)


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Is it legal/possible to request a flight-path change from Domestic to International minutes after take-off, for a privately owned jet?
This is related to the recent escape of Carlos Ghosn from Japan. While we don't know the details yet, M. Ghosn allegedly boarded a private plane from a small airport near Osaka [and probably in a kind of "luggage"!].
In this event, it seems the private plane was aimed to travel internationally. But that brings the question anyway:
Would the pilot of a private plane be authorized to change their destination after take-off, and, more specifically, request to travel to a foreign destination, while initially, (before take-off) the plane was supposed to reach a domestic destination?
Probably not the case in this escape story, but since there is much less passengers verification on domestic flights, allowing the flight-path change (for a private plane) would make things much easier for someone (wealthy) who wants to evade a country.

This may depend on the destination. For example to enter the US, the pilot must fill out (in advance) information on every passenger, port of entry, etc at least 60 minutes prior to departure. Crossing the ADIZ requires an IFR or DVFR flight plan filed at least 15 minutes prior to entry (which may be done from the air). Getting out of the US ADIZ is a similar process. I'm not sure about the Japan ADIZ procedures. This is, of course, assuming the pilot does everything legally to get an illegal passenger out of a country, which is a big "if".

The question is more about the ability to change the destination from domestic to international after take-off, not the formalities to enter this or that country. I guess if it is possible, the pilot will want to reach first any country where the illegal passenger will not be arrested.

@RingØ, if the crime is not political, but something most countries agree on being a crime like fraud, the illegal passenger will probably be arrested anywhere if found.

Generally speaking, ATC doesn't care who you are or where you're going. Their only job is "a safe, orderly and expeditious flow of traffic." If you request to amend the destination on your flight plan, they'll just type it into their computer and give back the new clearance it spits out. Diverting is a fairly routine thing, actually, especially when bad weather is afoot. If they even ask why, it's to make sure it's not due to an emergency or urgency. What (if anything) happens once you're safely on the ground at that new destination is someone else's problem.
That said, the militaries of many countries may take exception to someone flying into their airspace without prior permission, which is a much more complicated topic.

And congrats in reaching 10k

It depends entirely on which country the pilot is coming from, and which country he's planning to go to.
If you're leaving a country that has more controls on its populace, like China or North Korea, I'm sure that it would be pretty difficult to just fly out of the country whenever you feel like it. But, in the US and a lot of other first-world countries, it's a lot less of a hassle. In the US, you do need a flight plan to leave the country, but you can file one in just a few minutes on the phone or with a tablet. In fact, you can take off without a flight plan, and as long as you file and activate your flight plan more than 15 minutes before you reach the ADIZ, you're good.
It's getting into a country that's more difficult. As mentioned in the comments, the US requires customs information to be filed at least an hour before departure. I'm sure that other countries have more stringent requirements. So, unless you plan on requesting asylum, you really need to plan ahead for your international flight.

The country you are leaving has a limited say in the matter. It takes 10 minutes to scramble a fighter jet, and the surface-to-air missiles are normally not ready either, so if your intentions don't become obvious too soon, they basically can't stop you any more. Instead countries that try to prevent people emigrating will try to make sure you can't fly together with your family and they'll take revenge on them (there was defection, sometime in the 60s IIRC, where three airline pilots in Czechoslovakia managed to their their families on each other's flights and diverted).

@JanHudec the OP asked if the pilot would be authorized to do it, not if they would get away with it.


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What are these red lights next to an airport runway?
What are these red installations at the end of the runway? They shine bright like a laser but I don't think they would install those near an airport.

Are you talking about the approach lighting (lights on the poles) or the PAPI/VASI (red lights near the end of the runway on either side)?

Please post the photo inline with your question so we don't have to follow links and so your question will make sense if the link dies. Since you seem to be asking about runway lights then use that term in the title rather than "things" and "airport".

You mention them being "bright like a laser", that's probably because they're designed to visible 5 miles (8 km) away at day and 20 miles (32 km) away at night ;)

See https://aviation.stackexchange.com/questions/5170/how-do-papi-lights-work for diagrams of the lamps.

These are VASI lights, which stands for Visual Approach Slope Indicator. When approaching a runway to land, an aircraft follows a specific glide slope. Usually, that slope is around -3 degrees.
These VASI-lights help the pilot visually verifying that they are not too low and not too high. There are a total of four lights, representing two bars.
Now you only see two reds on the VASI, but there is also another color, that you will never get to see, except if you sit in a cockpit of a plane: White. Using this two colors, the VASI tells pilots if they are approaching the runway too high or too low.
The VASI works analog, so it does not know how high a plane is and it's position and changes lights accordingly. Both red and white light at the same time and by using a lens-mechanism, the pilots gets to see the correct lights.
There are three color codes of a VASI:

Source
When both the VASI-bars are red, as in your picture, the plane is too low and needs to pitch up. Red and white means on glidepath and two whites mean too high and the pilot needs to descend faster.
There's also a mnemonic to remember the (very easy tbh) color codes:

White over White, you're high as a kite.
Red over White, you're alright.
Red over Red, you're dead.
White over Red, unsaid.

(White over red is no color code actually, because you would have to fly inverted to get it, that's why it's "unsaid".
Here's how a VASI-light looks close-up:

Source

"When both the VASI-bars are red, as in your picture, the plane is too low and needs to pitch up."
"pitch up" is not correct - you would instead add more throttle to stop the descent, or climb even, while maintaining the same landing attitude.

The sentence, "The VASI works analog, so it does not know how high a plane is and it's position and changes lights accordingly." is confusing and makes it sound as though analogue electronics is involved. It just works with fixed optics (lamps, filters and lenses) to show red below a certain angle and white above that angle. +1 for the rest.

Not very helpful mnemonic where both "white over white" and "red over white" might rhyme with "high as a kite" or "you're alright".

@CrossRoads Airplane longitudinal control: pitch or power?

Power. See Jan Hudec's answer on 2 April 2014, and also the referenced e-book. I was trained by a Vietnam era C130 pilot, who now flys a Piper Arrow and a Piper Lance.  Keep the same pitch attitude, add some power if you are getting low.  VFR you can get away with more sloppiness - get low, pull up, overpower the plane to get back on glideslope for a panic climb away from lights or terrain or whatever, but IFR following the glideslope (and perhaps GPS VNAV, I haven't gotten there yet with my new Avidyne GPS/NAV/COM, but I fly approaches like I was flying IFR for smooth approaches.

That is a VASI (visual approach slope indicator) system. It is used by aircraft to verify their approach angle when on final approach.
https://en.wikipedia.org/wiki/Visual_approach_slope_indicator


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Who is responsible to remove the landing gear pins in an airliner?
On a recent flight the airplane had to turn back, because the nose gear could not be retracted. Upon landing inspection it was found that the landing gear pin had not been removed.

Who is ultimately responsible to notice something like that?
Are there sensors indicating to the cockpit if the pins are present or not?
Are the pins required for push-back? In that case the pilots could not have spotted it during walk-around, correct?

In short, how can something like this happen and who is to blame?

Who: Why does the headset man not get on the tractor?, sensor: What item is a pushback operator holding up after pushback?, and in genereal: How is the pushback tug connected to the airliner?

Normally there are no indications pins are installed in the cockpit. Forgetting to take them out isn't really a safety issue, more of an expense.
Ultimately the Pilot In Command is responsible, as one of the items to check on the walkaround is that pins are removed, whether by ground crew or the pilot doing the walkaround. They are normally stowed on board, so at some point the PIC will need to confirm that all safety pins are removed and are aboard the aircraft.
On the CRJ200 there were 3 pins for the main gears, one for the nose gear doors (because they were hydraulically operated) and one for the Air Driven Generator (right beside the nose gear bay), and whomever did the walkaround would present to the cockpit with a hand full of pins and say "five pins", before stowing them. It was up to the PIC in the end to confirm all 5 pins were there.
I know of a Global Express that departed Montreal with the nose gear pin installed. Rather than return and land overweight or fly around burning off fuel just to return, the crew continued to destination with the gear down and speed limited to 250kt. It was likely the First Officer who did the walkaround and forgot it, and he/she certainly would have been in the dog house, but ultimately the Captain is on the hook.

In our Boeing 737s the gear pins are stored in a rack at the front the electronics panel and are checked as part of the Before Start Checklist “gear pins……….1,2,3 removed.” We physically count them at the start of our flying day. (They aren’t part of the transit before start checklist).

Why continuing to destination with gear down might be a bad idea.

@Bianfable The Global crew made all the calcs and decided continuing wasn't a safety issue. IIRC it had the mains retracted with just the nose gear extended.

Thank you, John! So does that mean that there is no pin installed during the push-back? Otherwise how would the removed pin be put into the cockpit? In this case it was a transatlantic flight, so I am sure it made sense to return to the airport.

It's possible some airplane could have a pin that has to be removed after the push-back, although I can't imagine what. It would have to be something that stays with the pushback tractor, and when the tractor operator removes it, he/she would have to hold it up and get a thumbs up from the pilot. This is a case where everybody missed a pin with the red REMOVE BEFORE FLIGHT ribbon hanging down, all the way through the push-back. You'd hope that the tug operator or a wing tip escort would notice as a final back stop, but evidently not. Still, the responsibility is with the Capt in the end.

@JohnK all Boeing and Airbus aircraft will be fitted with a bypass pin for pushback! A bypass pin is used during towing or pushback to disengage the aircraft's nose wheel steering, preventing hydraulic pressure from steering the nose wheel. It protects the aircraft's systems during ground handling. The pin, is removed after pushback and shown/waved to the  flight crew by the ground staff.

@tedioustortoise thanks. The RJs used captive pins in the scissors links.  In either case, if they are forgotten you find out right away as you as you try to taxi.


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When do you change from HOT back to COLD carb heat on a Cessna 150
I'm currently doing a PPL in the UK and have only flown around 5 hours with an instructor. Training aircraft is a Cessna 150.
One thing I'm finding confusing is when carb heat should be set to COLD. But moreover, when would you switch from FULL HOT back to FULL COLD?
The book I'm learning from is Pooley's "Flying Training" Volume 1. This book states in Exercise 4g

Carburettor ice can occur at outside temperatures of +25C or more ... Noticeable effects include a drop in rpm, rough running, possible engine stoppage.

The suggestion is you would apply FULL HOT carburettor heat in such situations, e.g. during rough running of the engine. This makes sense.
It doesn't, however, say when you would go back to FULL COLD. My assumption here is just whenever the condition has been recovered. For instance if the engine is rough running you could apply FULL HOT carb heat, wait for the engine to run smoothly again, and then go back to FULL COLD?
The only scenario I've come across where you'd explicitly use COLD is taxiing. The reason given by the book is

the hot air for the carb heat is supplied from around the engine exhaust and is unfiltered ... For this reason it us usual to taxi with the carb heat control in the FULL COLD position to avoid introducing dust and grit into the engine.

The book also states in the Airwork section for Exercise 4g

Using Carb heat as a precaution.
When reducing power to IDLE: Set carb heat to FULL HOT. Throttle closed.
When about to increase power: Set carb heat to FULL COLD (if hot air to carburettor no longer required).

Sentences such as "if hot air to carburettor no longer required" seem ambigious. It doesn't tell me under what scenarios that would be acceptable. Many sections of the book will say "apply FULL HOT carb heat" but never state when you would change back to COLD, i.e. you'd carry on the entire flight with FULL HOT carb heat, which I know even from a common sense perspective cannot be true.
Some searches I've done on this subject such as

https://www.reddit.com/r/flying/comments/1vg9xl/when_do_you_use_carb_heat/
Should I have carb heat on for landing in a C152?

make it seem that this is a debatable subject, which I find astonishing given how important this control supposedly is.
Any clarification would be appreciated. Please take into consideration I am relatively new to flying and trying to learn from those with relevant experience.

Two key issues:

Carb heat delivers unfiltered air from its side of the airbox under the carb.
Few light aircraft actually measure the temperature of the air in the carb. Carb Air Temperature is often a feature of large radial engined aircraft, but not on small piston engine airplanes. So you can't know how much heat you're applying at intermediate positions.

Another minor issue is the higher temperature of the heated air reduces engine power, about as much as turning off a magneto (why you get about the same RPM drop as during a mag check), so takeoff/climb performance is reduced.
With unfiltered air, you don't want the airplane running with carb heat on any longer than necessary, because the unfiltered air means the engine is breathing dust, which outdoors means silica particles, which gets into the oil and makes it abrasive. Over the very long term it increases engine wear, so operation on unfiltered air is generally minimized, especially at low altitude. In WWII desert operations, piston engine fighters, that normally had no air filters, had to use very bulky "desert" air filters to keep the engines from being worn out in no time due to fine sand, which turns the engine oil into lapping compound after a while (some of what the engine breathes always ends up in the oil as particles settle on the cylinder walls).
Because you don't know the actual air temperature, it becomes a binary choice: either full hot or full cold. If you apply partial carb heat, you may only be bringing the air temperature into the ideal range for icing without realizing it.
So, if there's evidence of carb icing, it's full on. How long? It's a judgement call, but longer than just the time it takes to make the symptom go away. The symptom may go away while there is residual ice on the carb throat and throttle plate, so add, say, 10 seconds or so. It's not cast in stone, because every airplane is different and you have no data to go on. 10 seconds, 15 seconds, it's not that big of a deal, and a little too long is better than not long enough. Just don't get carried away.
In cruise, it's normal practice to just add full carb heat periodically for 10 seconds, around every 15 minutes or so, just in case ice is beginning to form.
If the engine has a constant speed propeller, power reductions don't create an RPM drop. If you are getting icing, it will show up as a reduction in manifold pressure even though you are in level flight and haven't touched the throttle.
Some engines are more susceptible to carb icing than others. Continentals (as the 150 has) have the oil sump behind the carburetor so the carb body gets little warming from the engine. Icing happens more easily; that is, the window of conditions is wider.
On Lycomings (which the 152 has), the carb is bolted to the bottom of the oil sump and the passages to the cylinders are cast right into the sump. The carb body is warmed by engine heat and carb icing is less common because the window of conditions for formation of ice is narrower.
Operationally, you treat them the same and use carb heat the same way. Full hot, for 10 or 15 seconds, then full cold.
If you have significant icing, when you apply heat the engine will likely stumble and run quite rough as the choke effect of the ice is made worse be the richer mixture caused by the hot air it's breathing. Adding throttle, to make the nearly-blocked throttle plate opening bigger, and even mixture leaning may be necessary to keep it running.
In general, if the engine starts to run rough and then quits, but then starts up normally later after descending, or on the ground, and it runs perfectly, it was almost certainly carb ice.
Welcome to aviation, a world that, like the marine world, is often shades of grey and judgement calls instead of go/no-go choices.


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Cost of a private pilot
I am looking at purchasing a plane and I am trying to get the best estimate possible of what the hourly cost is going to be. I can’t seem to find any information on the cost of a pilot and I’m hoping the community can help with an estimate. Here’s the plan, I want to purchase a piper navajo chieftain for my family to use for shorter trips in our region (Northeast) and I want a hire a pilot to fly us. I know there are a bunch of variables with this question (insurance, skill level, experience w the aircraft) that will play into the cost. I’m looking for an hourly estimate I think? I’m assuming I pay for them to stay and other expenses if it’s an overnight trip? I’m just trying to get clarification to make a final hourly cost estimate. I thank you in advance and appreciate any info. I am 100% not as knowledgeable as anyone on here, so dumb it down for me please. Also, if I’m missing anything glaring please don’t hesitate.

Keep in mind that "private pilot" is a class of license that doesn't allow carrying passengers for compensation. In this scenario you would have to hire a pilot with a "commercial pilot" license.

There are dozens of factors that play into an 'hourly rate', far too many for someone to list here and come up with an estimate. Instead, find a small aircraft charter company and ask them the cost a charter for your typical use case. When you've recovered from the shock, treat this as a ball park figure. Do not assume that you can necessarily improve on it.

Where is your region? North-East USA? North-east UK? North-East Europe? This can have a substantial impact on your costs.

$200/hr just for fuel at 32 gal/hr. Triple that to get the overall fixed and hourly operating costs if it's used moderately. Maybe another 60 dollars overall for the pilot incl his/her expenses.  You can figure on 600 to 1000 dollars per hour. Not an answer because I'm just spitballing. So many variables

Northeast US. Sorry about that. I didn’t realize the pilot would need a commercial license to fly my plane, I’m sure that is going to add to the cost dramatically. My base estimate so far is about $875 hour all-in. I’ll reach out to the local charter company I currently use and ask their opinion, I know they have a few younger pilots on staff that would love the hours, I just don’t want to get taken to the cleaners by them.

Have you considered getting yourself a private pilots license? Then you could fly your family wherever you wanted to go!

Normally you wouldn't buy your own airplane and then hire a pilot occasionally; the pilot would have their own aircraft that they maintain and are familiar with and use regularly, and you'd just charter a flight when needed. You might want to just look around and see what kind of charter flight services are available near you -- in the long run it's likely cheaper than buying your own airplane.

@DarthPseudonym or you buy the aircraft AND hire the pilot to work for you as an employee, but that requires a LOT of flight time to be economical and is typically only feasible for larger corporations and rich people with international commitments.


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Which airlines allow you to gain hours with them by paying them
As a fresh grduated pilot is there any airline that you can pay them to fly with them without a salary just to build hours?

Voting to close because it's too broad. There's a whole list on Wikipedia.

There are pay to fly services, however regulations require a minimum number of hours before you can do any kind of part 121 or part 135 work. So while you can get some extra hours in Jets by paying them that way or turbo props or whatever else you’re looking for, it’s not recommended. Probably the best starting gate once you have a commercial pilot certificate is just doing flight instruction work until you gain the required 1500 hours.  After that you should have offers for most of the regional carriers to work for them as a first officer.

None. It doesn't work that way. Airlines have employees, not volunteers or indentured servants flying their aircraft, and the law requires that employees be paid. Not always paid very much, but "flying for free" doesn't exist at any airline I've ever heard of. And I wouldn't want to ride on any that had such a program.

Incorrect. This is called pay to fly, is prevalent in Europe and Asia, especially with wet lease operators.

Pay to get hired was big with the US regionals in the 90s when there were more pilots than jobs.  It's only stopped with the growing shortage of crews over the last 15 years.  If you peruse old pilot bulletin board posts like on PPrune from the late 90s there is a lot of bitter discussion over the practice.

@user71659  That is frightening.  I wonder what the safety record is at such operations.  No, actually, I suspect it's an easy guess....


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Why was there an increase in the number of airline accidents in 90s?
According to this Aviation Safety Network article and dataset there was a significant drop in the number of airline accidents in the early 80s comparing to the years before - from ~50 per year down to ~30 per year. However, in the late 80s and the 90s this number increased back to ~50 and stayed at this level until early 2000s. Is there any explanation for the sharp increase of the accidents in the late 80s and the 90s? I see the number of flights increased linearly throughout the years, so this isn't the factor that explains the accident statistics.

Just the pure number of accidents isn't a good indicator of safety. Accident rates have decreased steadily even through the 90's and 2000's. The better statistic would be to look at number of accidents per million flights or per million hours. That will correlate with the number of total flights.

Two factors come to mind.  The 90s saw the rise of discount carriers, and Regional Jets, both involving sketchier maintenance and less experienced crews compared to mainline.

The ASN dataset varies from the traditional definition of aviation accident by including intentional acts, namely hijackings, bombings and shootdowns. Therefore you have to consider the political situation at the time, i.e. Cold War, Soviet-Afghan war, wars after fall of the Soviet Union, etc. It also is worldwide, many statistics specifically exclude Soviet-made aircraft and only look at Western-built models. There was a mass retirement of Soviet types in the early 2000s.

Also you're looking at the number of 14 passenger+ planes crashed and are dividing by number of air carrier flights. This misses trends in corporate aviation, many charter flights/cargo charters, air taxi operations, etc.